Hansen's smoking gun

Remember when climate change was something our grandchildren were going to have to deal with?

That was then.  Today, we’re in a different world.  It’s impossible to say exactly when we made the transition, though the usual sense is that it occurred sometime between, say, 2010 – a catastrophic  year in which, for example, Pakistan (as in “nuclear-armed Pakistan”) suffered floods so epic and destructive that they actually pushed the population down the ladder of development — and, say, 2012, the year in which the dust-bowlification of the American heartland became a fact on the ground.

James Hansen uses a more scientific dating system.  In his new paper, Public Perception of Climate Change, written with Makiko Sato and Reto Ruedy and published in Proceedings of the National Academy of Science on August 6th, he proceeds by setting a formal baseline, which he does in terms of the three decades from 1951 to 1980.  These were the last of the old epoch.  Since then, we’ve no longer been in the Holocene, but rather have been busily drilling ourselves further and further into the Anthropocene.

Or, to use Hansen’s favorite metaphor, we’ve been busily loading the “climate dice.”  Back in the Holocene, two faces of the dice were (red) “hot,” two were (white) “average,” and two were (blue) “cold.”  Today,

“we find that actual summer-mean temperature anomalies over global land during the past decade averaged about 75% in the “hot category”, thus midway between four and five sides of the die were red.”

But that’s not all.

“A more important change is the emergence of a subset of the hot category, extremely hot outliers, defined as anomalies exceeding [3 standard deviations]. The frequency of these extreme anomalies is about 0.13% in the normal distribution, and thus a typical summer in the period of climatology [Hansen’s name for the world that ended with his 1951 to 1980 baseline period] would have only about 0.1-0.2% of the globe covered by such hot extremes. We show that during the past several years the portion of global land area covered by summer temperature anomalies exceeding [3 standard deviations] has averaged about 10%, thus an increase by about a factor of 50 compared to the period of climatology.”

A factor of 50, and a statistical smoking gun.  Really?  Hansen does not hesitate:

“Recent examples of summer temperature anomalies exceeding [3 standard deviations] include the heat wave and drought in Oklahoma, Texas and Mexico in 2011 and a larger region encompassing much of the Middle East, Western Asia and Eastern Europe, including Moscow, in 2010.”

We’re not in Kansas anymore.  Or if we are, it sure is a lot hotter than it used to be.  And Hansen is violating the traditional rules of “scientific reticence” by pointing it out.  According to The Economist, this has “caused a stir among those who feel that scientific papers should be dispassionate in their delivery of the evidence.”  Interestingly, though, this rather ritualistic disclaimer is followed by a straight, just-the-facts-ma’am, report on the paper and its methods.  Which are, it should be explicitly noted, not based on any climate model, but rather on a rather straight-forward statistical analysis.  There’s no denialism, not even a hint, though it should be said that The Economist, back in days of yore, would have insisted on one.

But that was then.  The point now is “to agree that it is real, and to think about the consequences.”

— Tom Athanasiou